1. Field of the Invention
The present invention relates a resin molding die for obtaining a molding product comprising an electronic part such as a semiconductor device, capacitor or inductor by injecting a resin into a cavity.
2. Description of Related Art
A package for a semiconductor device such as LSI is formed by mounting a device formed as a chip on a lead frame or the line and then integrally encapsulating the device by a molding resin or the like.
In a case of integrally encapsulating a device by a molding resin or the like, a transfer molding apparatus has been used generally and a molding product is manufactured to a predetermined shape by setting a predetermined resin molding die to the transfer molding apparatus.
In a case of manufacturing a semiconductor device in the prior art, a package is constituted by mounting a chip-shaped device to a lead frame made of a 42 alloy (Fe--Ni alloy of 42% Ni), applying wirings by bonding wires, which is set to a resin molding die of a transfer molding apparatus and transferring and injecting a mold resin such as epoxy resin into a cavity of a die.
In the resin molding die used herein, an insert block having a cavity in which a resin is injected by way of a gate and a base block for incorporating and holding the insert block are disposed, respectively, to upper and lower dies, each of which is made of an iron-based hard metal hardened to a predetermined number of hardness.
Upon transfer molding, the upper die and the lower die are attached respectively in a separated state to a platen of the transfer molding apparatus, and a lead frame mounted with a device is set, for example, on the lower die heated to a predetermined temperature (150.degree. C.-200.degree. C.).
In this case, the device on the lead frame is disposed at a position for the cavity of the die.
Subsequently, a tablet-shaped resin is injected into a pot disposed to the lower die, and the upper die and the lower die are clamped.
The load on the die clamping is for example, about 196 kN per one lead frame such that a gap is not opened by the injected resin (about 7.8 MPa).
Further, slight elastic deformation is caused by the clamping load to each of contact portions between the upper and the lower dies and tie bars of the lead frame, to eliminate the gap for the contact portions thereby preventing leakage of the resin.
Then, the tablet-shaped resin is melted in the state of clamping the upper and the lower dies under such a load, and then the resin is injected by way of the gate into the cavity by pressing a plunger.
Thus, the periphery of the device on the lead frame disposed in the cavity can be covered with the resin, to complete a molding product conforming the shape of the cavity.
For the resin molding die, an iron-based hard alloy having a Vickers hardness Hv=about 58-63 and an Young's modulus of about 2.times.10.sup.12 dyn/cm.sup.2 is used with a view point of durability in use.
Further, vapor deposition of hard chromium or titanium nitride is applied to the surface of the insert block for improving the wearing resistance and mold releasability.
In recent years, it is considered a resin molding die having a structure capable of detaching the gate and using a super hard alloy for the gate, intended for the improvement of the durability in use.
However, the resin molding die described above involves the following problems.
That is, upon resin molding, if the clamping load between the upper and lower dies is lower than a predetermined value, injected resin leaks. For instance, in a case of a semiconductor device, the resin leaked to the lead portion of the lead frame forms burs to bring about disadvantage in subsequent steps.
That is, the clamping load has to be applied between the upper and lower dies to such an extent as capable of ensuring elastic deformation in an amount enough to inhibit the leakage of the resin at a portion of contact between the upper and lower dies and the tie bars of the lead frame.
Since the existent resin molding die is constituted with a hardened iron-based hard alloy, a press mechanism equipped with a large scaled hydraulic cylinder or the like is necessary in order to obtain an elastic deformation amount required for the portion of contact, which brings about a problem of increasing the size of the molding machine.